The proliferation and differentiation of cells in multicellular organisms is subject to a highly regulated process. A distinguishing feature of cancer cells is the absence of control over this process; proliferation and differentiation become deregulated resulting in uncontrolled growth. Significant research efforts have been directed toward better understanding this difference between normal and tumor cells. One area of research focus is growth factors and, more specifically, autocrine growth stimulation.
Growth factors are polypeptides which carry messages to cells concerning growth, differentiation, migration and gene expression. Typically, growth factors are produced in one cell and act on another cell to stimulate proliferation. However, certain malignant cells, in culture, demonstrate a greater or absolute reliance on an autocrine growth mechanism. Malignant cells which observe this autocrine behavior circumvent the regulation of growth factor production by other cells and are therefore unregulated in their growth.
Study of autocrine growth control advances understanding of cell growth mechanisms and leads to important advances in the diagnosis and treatment of cancer. Toward this end, a number of growth factors have been studied, including insulin-like growth factors (“IGF1” and “IGF2”), gastrin-releasing peptide (“GRP”), transforming growth factors alpha and beta (“TGF-a” and “TGF-b”), and epidermal growth factor (“EGF”).
The present invention is directed to a recently discovered growth factor. This growth factor was first discovered in the culture medium of highly tumorigenic “PC cells,” an insulin-independent variant isolated from the teratoma derived adipogenic cell line 1246. This growth factor is referred to herein as “GP88.” GP88 has been purified and structurally characterized. Amino acid sequencing of GP88 indicates that GP88 has amino acid sequence similarities with the mouse granulin/epithelin precursor.
Granulins/epithelins (“grn/epi”) are 6 kDa polypeptides and belong to a novel family of double cysteine rich polypeptides. U.S. Pat. No. 5,416,192 (Shoyab et al.) is directed to 6 kDa epithelins, particularly epithelin 1 and epithelin 2. According to Shoyab, both epithelins are encoded by a common 63.5 kDa precursor, which is processed into smaller forms as soon as it is synthesized, so that the only natural products found in biological samples are the 6 kDa forms. Shoyab et al. teaches that the epithelin precursor is biologically inactive.
Contrary to the teachings of Shoyab et al., the inventor's laboratory has demonstrated that the precursor is not always processed as soon as it is synthesized. Studies, conducted in part by this inventor, have demonstrated that the precursor (i.e., GP88) is in fact secreted as an 88 kDa glycoprotein with an N-linked carbohydrate moiety of 20 kDa. Analysis of the N-terminal sequence of GP88 indicates that GP88 starts at amino acid 17 of the grn/epi precursor, demonstrating that the first 17 amino acids from the protein sequence deduced from the precursor cDNA correspond to a signal peptide compatible with targeting for membrane localization or for secretion. Also in contrast to the teachings of Shoyab et al., GP88 is biologically active and has growth promoting activity, particularly as an autocrine growth factor for the producer cells.
Diagnosis of cancer often requires sampling a biopsy of a tissue suspected of being tumorigenic, testing the tissue sample to determine if a tumor marker is present, and determining if the tissue sample is tumorigenic. Biopsy procedures can be risky and painful depending on the location of the tissue and the condition of the patient. In addition, the trauma inflicted by biopsy procedures may increase the risk of malignancy. A study reported in the British Medical Journal identified biopsy as the strongest risk factor for testicular cancer. Swerdlow et al., BMJ 1997;314:1507. Biopsy has also been identified as a risk factor in breast, liver, and other cancers. In addition, a study conducted at the Johns Hopkins University concluded that misdiagnosis following biopsies occurs at a significant rate. Kronz et al., Cancer: Dec. 1, 1999, vol. 86, no. 11 pp 2426–2435. Misdiagnosis may be due, in part, to the small sample sizes obtained from needle biopsies and other procedures that capture only small tissue samples. Small biopsy sample sizes reduce patient risk. Id. However, the risk of misdiagnosis increases when only a small tissue sample is utilized. Id.
What is needed are new methods and kits for diagnosis, treatment, and prevention of cancer, and particularly methods and kits that avoid risks associated with biopsy of tissue.